This is a great question and I have wondered this many times myself. There are many comments about the downfalls of bridging amps. Why? What is the difference between bridging and monoblocks?
True Monoblocks vs Switchable Stereo to Mono Amps
are there any sonic advantages and to what degree in an amp designed from the ground up as a Monoblock, for example the older Jeff Rowland Model 7, vs using 2 Jeff Rowland Model 1s which are stereo amps which are mono switchable. it seems if the sonic benefits are minimal, then the advantage of having 2 Stereo amps would be a plus in the event 1 amp went down.